Wires and cables and like conductors used for the transmission of radio frequency signals and signals of other frequencies suffer from well-known interference problems. Essential to the control of such interference in electrical wire and cable conductor systems is the ability to provide shielding. Actually, such wires and cables may transmit interference, which must be contained, while at the same time they may pick up interference from outside sources, e.g., from other electronic devices. Consequently, since all wire and cable, when in use, is a potential source of electrical noise, a means of containing these bothersome emissions is important if the wire and cable are to perform efficiently and effectively.
In addition, wire and cable conductors are affected by many external sources such as motors, office equipment, fluorescent lights, other unshielded wires and cables, power transmission lines, cellular phones and numerous other sources.
Wire and cable have been proposed and are available with shielded systems which are based on metal, such as copper.
Since practically all of the wire and cable applications require some degree of flexibility, especially when installing the wires and cables into a network or system, shielding materials must not adversely affect the desired flexibility. As a result, solid metal forms, which might, indeed, provide excellent shielding, e.g., tubing, cannot be used for most purposes. Consequently, current practice permits the use of braided metal wires around the conductive core. The metal wires most commonly used for this purpose are copper, tin-plated copper, nickel-plated copper, and silver-plated stainless steel. The braid configuration depends upon the frequencies involved. For example, copper spiral wrapping is poor for frequencies above 100 KHz, whereas braided copper strands provide shielding of relatively good efficiency in that range. It is also important that the shielding be capable of grounding effectively.
While, therefore, braided shields heretofore used are relatively effective, they generally tend to suffer from one or more disadvantages. For example, they may be undesirably heavy, lack sufficient flexibility, have poor fatigue resistance, and be susceptible to breaking under certain circumstances.
It is, accordingly, an object of the present invention to provide a braided shield for wire and cable conductors which avoids the drawbacks and disadvantages of braided shields heretofore employed.
It is another object of the invention to provide a braided shield of the character indicated, which is relatively light in weight, has high flexibility, enjoys good fatigue resistance, and is free from a tendency to break.
It is a further object of the invention to provide a composite conductor assembly which includes an improved braided shield.